clc;
clear;
A=[6,1,4,2,1;
   3,0,1,4,2;
   -3,-2,-5,8,4];

rank(A)
disp('--------------------------------------------')
iA=pinv(A)
norm(A*iA*A-A),
norm(iA*A-A'*iA'),
norm(A*iA-iA'*A')